1. Field of the Invention
The present invention relates to movable body apparatus, exposure apparatus, exposure methods, and device manufacturing methods, and more particularly, to a movable body apparatus including a movable body which is movable along a two-dimensional plane, an exposure apparatus equipped with the movable body apparatus, an exposure method in which an energy beam is irradiated on an object on the movable body to form a predetermined pattern, and a device manufacturing method which uses the exposure apparatus or the exposure method.
2. Description of the Background Art
Conventionally, in a lithography process for manufacturing electron devices (microdevices) such as semiconductor devices (such as integrated circuits) and liquid crystal display devices, exposure apparatuses such as a projection exposure apparatus by a step-and-repeat method (a so-called stepper) and a projection exposure apparatus by a step-and-scan method (a so-called scanning stepper (which is also called a scanner) are mainly used.
In these types of exposure apparatuses, the position of a wafer stage which moves two-dimensionally, holding a sensitive object (hereinafter generally referred to as a wafer) such as a wafer or a glass plate on which a pattern is formed, was measured by a laser interferometer in general. However, requirements for a wafer stage position control performance with higher precision are increasing due to finer patterns that accompany higher integration of semiconductor devices recently, and as a consequence, short-term variation of measurement values due to temperature fluctuation and/or the influence of temperature gradient of the atmosphere on the beam path of the laser interferometer can no longer be ignored.
To improve such an inconvenience, various inventions related to an exposure apparatus that has employed an encoder having a measurement resolution at the same level or better than a laser interferometer as the position measuring device of the wafer stage have been proposed (refer to, for example, U.S. Patent Application Publication No. 2008/0088843). However, in the liquid immersion exposure apparatus disclosed in U.S. Patent Application Publication No. 2008/0088843 and the like, there still were points that should have been improved, such as a threat of the wafer stage (a grating installed on the wafer stage upper surface) being deformed when influenced by heat of vaporization and the like when the liquid evaporates.
To improve such an inconvenience, for example, in U.S. Patent Application Publication No. 2008/0094594, as a fifth embodiment, an exposure apparatus is disclosed which is equipped with an encoder system that has a grating arranged on the upper surface of a wafer stage configured by a light transmitting member and measures the displacement of the wafer stage related to the periodic direction of the grating by making a measurement beam from an encoder main body placed below the wafer stage enter the wafer stage and be irradiated on the grating, and by receiving a diffraction light which occurs in the grating. In this apparatus, because the grating is covered with a cover glass, the grating is immune to the heat of vaporization, which makes it possible to measure the position of the wafer stage with high precision.
However, it was difficult to employ the placement of the encoder main body related to the fifth embodiment of Patent Application Publication No 2008/0094594 in the case of measuring positional information of a fine movement stage in a so-called coarse/fine movement structure, which includes a coarse movement stage that moves on a surface plate and a fine movement stage that holds a wafer and moves on the coarse movement stage. This was because the coarse movement stage placed above the surface plate interferes with the measurement beam from the encoder main, body which is irradiated on the fine movement stage placed further above.
Further, while it is desirable to measure positional information of the wafer stage within the two-dimensional plane the same as the exposure point on the wafer surface when exposure to the wafer on the wafer stage is performed, in the case when the wafer stage is inclined with respect to the two-dimensional plane, measurement errors which are caused by a height difference of a wafer surface and a placement surface of the grating would be included, for example, in measurement values of an encoder which measures the position of the wafer stage from below.